<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Dear Ramanish Singh, <div class=""><br class=""></div><div class="">if I would know the answer I wouldn’t do any calculations anymore, but rather use intuition instead ;) </div><div class="">However, I GUESS that your observation is not due to phase coexistence (I have a lot to say here, </div><div class="">but would be way beyond the purpose of this mailing list), but more due to an underestimation of the </div><div class="">density by DFT. Are you using any form of dispersion correction? Long story short, beside the usage </div><div class="">of vdW correction, I recommend to relax the cell instead of over pressurizing it. </div><div class=""><br class=""></div><div class="">Best, </div><div class="">Thomas Kühne</div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">Am 24.09.2019 um 16:27 schrieb Ramanish Singh <<a href="mailto:sing...@umn.edu" class="">sing...@umn.edu</a>>:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Thanks Thomas Kühne. <div class="">I am simulating liquid Iodine close to the Vapor Liquid coexistence curve using BLYP functional. I used experimental density to find the V for my NVT simulations. But now I suspect there can be a two phase system in my box and that's why the pressure is becoming negative. </div><div class="">So instead of the experimental density I am using slightly higher density(~10 percent higher) to make sure it is in the liquid phase at that Temperature. What are your thoughts on this?</div><div class=""><br class=""></div><div class="">Thanks,</div><div class="">Ramanish Singh<br class=""><br class="">On Monday, September 23, 2019 at 12:59:41 PM UTC-5, tkuehne wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div style="word-wrap:break-word" class="">Dear Ramanish Singh, <div class=""><br class=""></div><div class="">minimal mispredictions within lattice constant and vectors </div><div class="">may entail large changes in the pressure. So observing a </div><div class="">rather large negative pressure is not necessarily indicative </div><div class="">of a problem. Beside that the usage of good basis sets and </div><div class="">tight SCF convergence is essential, it is hard to say anything </div><div class="">specific without detailed knowledge on what you plan to do. </div><div class=""><br class=""></div><div class="">Best, </div><div class="">Thomas Kühne</div><div class=""><br class=""><div class=""><div class=""><blockquote type="cite" class=""><div class="">Am 23.09.2019 um 18:01 schrieb Ramanish Singh <<a href="javascript:" target="_blank" gdf-obfuscated-mailto="uNOR6wcxBAAJ" rel="nofollow" onmousedown="this.href='javascript:';return true;" onclick="this.href='javascript:';return true;" class="">si...@umn.edu</a>>:</div><br class=""><div class=""><div dir="ltr" class="">Hi,<div class=""><br class=""></div><div class="">I am simulating a system of Iodine atoms using BLYP functional in the NVT ensemble.</div><div class="">But when I am calculating the pressure, using STRESS_TENSOR ANALYTICAL in the FORCE_EVAL section, my pressure (average of the xx,yy and zz elements) is coming out to be negative which is far from the experimental pressure at that density and Temperature. </div><div class="">I can not figure out why this is happening. </div><div class=""><br class=""></div><div class="">Thanks,</div><div class="">Ramanish Singh</div></div><div class=""><br class=""></div>
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